This invention relates to a pedestal with an extended function, serving as a base on which a semiconductor exposure apparatus, for example, is to be mounted, and also to an exposure apparatus having such pedestal.
In order to meet further miniaturization of a semiconductor device, more strict requirements have been applied in respect to a vibration environment of a semiconductor exposure apparatus. Particularly, in semiconductor exposure apparatuses called a xe2x80x9cscannerxe2x80x9d wherein a wafer stage for carrying a semiconductor wafer thereon and a reticle stage for carrying a reticle (original of a circuit pattern) thereon are scanningly moved in opposite directions in synchronism with each other and at a predetermined velocity ratio and wherein the exposure of the semiconductor wafer is performed during such scan motion, if the synchronous scan motion is disturbed by any vibration, the quality of a product IC is directly degraded. Namely, such scanner is very sensitive to vibration of a floor, for example.
Conventionally, however, no specific design or construction has been made in relation to vibration of a floor within a clean room where a semiconductor exposure apparatus is to be placed. Therefore, such floor vibration causes a critical influence to the scanner. In consideration of it, when a semiconductor exposure apparatus is mounted in a clean room, some measures are taken to substantially reinforce the floor. More specifically, a large base called a xe2x80x9cpedestalxe2x80x9d such as denoted at 2xe2x80x2 in FIG. 2 is used, and the entire semiconductor exposure apparatus 1 is placed thereon. In other words, a very large floor covering for mounting the semiconductor exposure apparatus 1 thereon is prepared. The pedestal thus functions as a base.
However, even if a pedestal having a large mass and an appropriate damping function is used to reduce the vibration to be transmitted to the scanner, it is not possible to completely intercept the vibration transmission. This is because the pedestal is to cover the floor area just to be occupied by the scanner. Namely, vibration can be amplified at the interface between the floor and the pedestal, and it can be transmitted from the pedestal to the semiconductor exposure apparatus. Further, as regards such vibration with which the clean room as a whole can be oscillated, use of a pedestal is not effective to reduce the vibration level.
On the other hand, the major structure of a semiconductor exposure apparatus is supported by an anti-vibration unit. As regards the types of such anti-vibration unit, there are two types: a passive type anti-vibration unit using passive springs or viscosity elements, and an active type anti-vibration unit having sensors and actuators, constituting a closed loop system. Recently, to meet strict vibration environment, the latter active type anti-vibration unit is used in many cases. Such active anti-vibration unit has a function for feeding back signals of sensors to an actuator. Also, it can be equipped with a feed-forward function for detecting floor vibration and driving an actuator while making appropriate compensation to the floor vibration. Moreover, it can be equipped with a reaction-force feed-forward function for driving an actuator in the active type anti-vibration unit on the basis of a driving signal of a unit which produces a large drive reaction force in the semiconductor exposure apparatus. The former feed-forward function is called a floor vibration feed-forward or ground vibration feed-forward. In order to attain this feed-forward function, it is necessary to measure vibration of the floor. Practically, to this end, a vibration sensor is provided in a mechanism component of the semiconductor exposure apparatus, which can be considered as being integral with the floor. A specific example is shown in FIG. 3. Denoted in FIG. 3 at 3 are gratings which are disposed on the floor of a clean room. Denoted at 4 is one pillar of a major structure of a semiconductor exposure apparatus. Denoted at 5 is a structural member which is rigidly connected to the pillar 4 of the major structure. Denoted at 6 is a vibration sensor which is mounted on the structural member 5.
It should be noted however that not only floor vibration but also any other vibration are present at the structural member 5 having the vibration sensor mounted thereon. Namely, local vibration may occur at the structural member 5. Alternatively, any local vibration produced at any other portion (not shown) may be transmitted to the structural member 5. The vibration sensor 6 may of course detect such vibration. This means that a noise other than a signal for the ground vibration feed-forward control can be mixed. Therefore, the effectiveness of the ground vibration feed-forward control based on an output signal of a vibration sensor, where floor vibration and any other local vibration of the structural member, for example, are mixed, is lowered and, thus, the anti-vibration effect to the floor vibration is degraded.
As described above, in semiconductor exposure apparatuses called a scanner, since vibration of a floor on which the exposure apparatus is placed directly influences the performance of the apparatus, a base called a pedestal may be used and the whole exposure apparatus may be mounted thereon. However, even use of such pedestal can not completely remove the vibration. On the other hand, semiconductor exposure apparatuses are generally equipped with an active type anti-vibration unit to meet further miniaturization of semiconductor chips. The active type anti-vibration unit can have a ground vibration feed-forward function for reducing transmission, into the exposure apparatus, of vibration of the floor where the semiconductor exposure apparatus is placed. However, such ground vibration feed-forward function is attained on the basis of a signal into which any local vibration other than the floor vibration can be mixed. Therefore, it is difficult to accomplish an effectual ant-vibration characteristic.
It is an object of the present invention to accomplish an effectual ground vibration feed-forward function in an active type anti-vibration system.
In accordance with an aspect of the present invention, there is provided a pedestal, comprising: a pedestal structure for serving as a base for mounting a certain mechanism thereon; and a vibration sensor embedded in or incorporated in said pedestal structure.
The vibration sensor may be operable to detect at least one of an acceleration and a velocity.
The vibration sensor may be operable to detect vibration in orthogonal three axial directions.
The pedestal may further comprise an active anti-vibration system provided in the mechanism.
An output of said vibration sensor may be used as a feed-forward signal for a ground vibration feed-forward control through said active anti-vibration system.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: a major structure; an active anti-vibration system for supporting said major structure; a pedestal on which said major structure is mounted through said active anti-vibration system; and a vibration sensor embedded in or incorporated in said pedestal.
An output of said vibration sensor may be used as a feed-forward signal for a ground vibration feed-forward control through said active anti-vibration system.
The apparatus may further comprise a controller, wherein, when an earthquake is detected by said vibration sensor, said controller controls the operation of said exposure apparatus on the basis of the detection by said vibration sensor.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.